Yep, I've done that before too. Volvo has a special tool to blow pecan shells through the combustion chamber to clean carbon. But the best I've personally seen...and this is real....a washer was dropped down an intake manifold. (v8) You could hear it banging around when the motor was started. The mechanic revs up the motor, pours in Uncle Bens Rice...a whole box....and the rice sweeps out the washer. This was before catalytic converters. probably wouldnt work today.

 

Bob Mears

Supermarine Spitfire